Garageband can use audiounits so if it doesn't use VSTs you could always use fxpansions wrapper. Also Reason is NOT a VST, It is a sequencer with built in instruments, samplers and FX (as it doesn't even record audio I wouldn't even classify it as a DAW), so you definitely can't run it from within garageband, although you can use rewire...

MacRumors attracts a broad audience
of both consumers and professionals interested in
the latest technologies and products. We also boast an active community focused on
purchasing decisions and technical aspects of the iPhone, iPod, iPad, and Mac platforms.